1. Field of the Invention
The present invention relates generally to the field of fabricating display panels. More particularly, the present invention relates to apparatuses and methods for forming displays wherein elements are placed on a template (also referred to as a donor substrate) and are thereafter transferred to a receiving substrate.
2. Description of Related Art
Fabrication of display panels is well known in the art. Display panels may be comprised of active matrix or passive matrix panels. Active matrix panels and passive matrix panels may be either transmissive or reflective. Transmissive displays include polysilicon thin-film transistor (TFT) displays, and high-resolution polysilicon displays. Reflective displays typically comprise single crystal silicon integrated circuit substrates that have reflective pixels.
Liquid crystals, electroluminescent (EL) materials, organic light emitting diodes (OLEDs), up and downconverting phosphor (U/DCP), electrophoretic (EP) materials, or light emitting diodes (LEDs) may be used in fabricating flat-panel display panels. Each of these is known in the art and is discussed briefly below.
Liquid crystal displays (LCDs) can have an active matrix backplane in which thin-film transistors are co-located with LCD pixels. Flat-panel displays employing LCDs generally include five different components or layers: a White or sequential Red, Green, Blue light source, a first polarizing filter, that is mounted on one side of a circuit panel on which the TFTs are arrayed to form pixels, a filter plate containing at least three primary colors arranged into pixels, and a second polarizing filter. A volume between the circuit panel and the filter plate is filled with a liquid crystal material. This material will rotate the polarized light when an electric field is applied between the circuit panel and a transparent ground electrode affixed to the filter plate or a cover glass. Thus, when a particular pixel of the display is turned on, the liquid crystal material rotates polarized light being transmitted through the material so that it will pass through the second polarizing filter. Some liquid crystal materials, however, require no polarizers. LCDs may also have a passive matrix backplane which is usually two planes of strip electrodes which sandwich the liquid crystal material. However, passive matrices generally provide a lower quality display compared to active matrices. Liquid crystal material includes, but is not limited to, twisted nematic (TN), Super TN, double STN, and ferroelectric. U/DCP and EP displays are formed in a similar fashion except the active medium is different (e.g., upconverting gas, downconverting gas, electrophoretic materials).
EL displays have one or more pixels that are energized by an alternating current (AC) that must be provided to each pixel by row and column interconnects. EL displays generally provide a low brightness output because passive circuitry for exciting pixel phosphors typically operates at a pixel excitation frequency that is low relative to the luminance decay time of the phosphor material. However, an active matrix reduces the interconnect capacitance allowing the use of high frequency AC in order to obtain more efficient electroluminescence in the pixel phosphor. This results in increased brightness in the display.
LED displays are also used in flat-panel displays. LEDs emit light when energized. OLEDs operate like the LEDs except OLEDs use organic material in the formation of the diode.
Regardless of the type of active medium used, displays are generally comprised of at least a substrate and a backplane. The backplane forms the electrical interconnection of the display and comprises electrodes, capacitors, and transistors in at least some embodiments of a backplane.
FIG. 1A illustrates a rigid display device wherein the active matrix display backplane 10 is coupled to a rigid substrate 12. Typically, the active matrix display backplane is also rigid. FIG. 1B shows another rigid display. There, the active matrix display backplane 10 is coupled to a rigid substrate 12 (e.g., glass). Also shown is a plurality of blocks 14. These blocks may be fabricated separately and then deposited into holes on substrate 12 by a process known as fluidic self assembly; an example of this process is described in U.S. Pat. No. 5,545,291. These blocks may each contain driver circuitry (e.g., MOSFET and capacitor) for driving a pixel electrode. The active matrix backplane includes transparent pixel electrodes and row/column interconnects (not shown) to electrically interconnect the blocks 14. The plurality of blocks 14 is coupled to the active matrix display backplane 10 and the rigid substrate 12. FIG. 1C shows a reflective display 16 coupled to a rigid substrate 12. FIG. iD shows a reflective display 16 coupled to a rigid substrate 12. A plurality of blocks 14 is coupled to the reflective display 16 and to the rigid substrate 12.
Placing elements, such as pixel drivers, on a rigid substrate is well known. Prior techniques can be generally divided into two types: deterministic methods or random methods. Deterministic methods, such as pick and place, use a human or robot arm to pick each element and place it into its corresponding location in a different substrate. Pick and place methods generally place devices one at a time and are generally not applicable to very small or numerous elements such as those needed for large arrays, such as an active matrix liquid crystal display.
Random placement techniques are more effective and result in high yields if the elements to be placed have the right shape. U.S. Pat. No. 5,545,291 describes a method that uses random placement. In this method, microstructures are assembled onto a different substrate through fluid transport. This is sometimes referred to as fluidic self-assembly. Using this technique, various blocks, each containing a functional component, may be fabricated on one substrate and then separated from that substrate and assembled onto a separate rigid substrate through the fluidic self assembly (FSA) process. The blocks which are deposited onto receptor regions of a substrate may include any of a number of different functional components, such as LEDs, pixel drivers, sensors, etc. An example of a particular type of block and its functional component is described in copending U.S. patent application Ser. No. 09/251,220 which was filed Feb. 16, 1999 by the inventor John Stephen Smith and which is entitled xe2x80x9cFunctionally Symmetric Integrated Circuit Diexe2x80x9d. This application is hereby incorporated herein by reference.
As noted above, FIGS. 1B and 1D illustrate a display substrate 12 with blocks 14 formed in the rigid substrate 12. These blocks 14 may be deposited through an FSA process. In the FSA process, a slurry containing the blocks 14 is deposited over the rigid substrate 12 and the blocks 14 rest in corresponding openings in the substrate 12.
FIG. 2 shows a block 14 and a circuit element (not shown) on the top surface 18 of block 14. Generally, blocks 14 have a trapezoidal cross-section where the top of the block is wider than the bottom of the block.
FIG. 3 shows block 14 in a recessed region of the rigid substrate 12. Between the block and the rigid substrate is an eutetic layer 13. The block has a top surface 18.
FIG. 4 shows a planar side view of a rigid substrate coupled to a rigid display backplane with a plurality of blocks between the display backplane 30 and substrate 12. The plurality of blocks are functionally part of the display backplane 30 and are deposited onto receptor regions of the substrate 12. Each block drives at least one transparent pixel electrode. The pixel is fabricated over a transistor which is fabricated in the block.
FIG. 5 shows a portion of an array in an active matrix display backplane. The control line rows 31 and 32 in this device are coupled to gate electrodes along a row and the control line columns 34 and 35 are coupled to data drivers which supply pixel voltages which are applied to the pixel electrodes. A column line 34 is connected to a source electrode of field effect transistor (FET) 36. Another column line 35 is coupled to a source electrode of FET 37. A row line 32 is coupled to the gates of both FETs 36 and 37. The drain of FET 36 is coupled through capacitor 38 to a transparent pixel electrode along the row 32 formed by FETs 36 and 37, and the drain of FET 37 is coupled through a capacitor to another pixel electrode along the row. In one typical example, the backplane may be formed by depositing blocks, using an FSA technique, into a rigid substrate (e.g., glass); each block contains a FET and a capacitor and is interconnected to other blocks by column and row conductors that are deposited onto the rigid substrate; and, the capacitor is coupled to a pixel electrode by another conductor that is deposited onto the rigid 20 substrate. The active medium (e.g., a liquid crystal) is deposited at least on the pixel electrodes which will optically change the active medium""s properties in response to the combined voltages or currents produced by the pixel electrodes. The active medium at a given pixel electrode 42 will appear as a square or dot in the overall checkerboard type matrix of the display. The actual size of the FETs and the pixel electrodes 42 are not now drawn to scale, but are shown schematically for the purposes of illustration. The interconnect between the rows and columns is comprised of flexible and conductive material. For example, the interconnect could be made of conductive metals. FIG. 6 shows a top view of a plurality of pixel electrodes 48 in a backplane 46.
While the foregoing explains generally how flat panel displays are created, there are several disadvantages inherent to the related art. Industry needs a cost effective, efficient, and practical method for transferring elements to substrates. Accordingly, it is desirable to reduce the cost and the time to produce a display by directly transferring blocks to a substrate.
The present invention provides methods and apparatuses for transferring elements from a reusable or disposable template into openings of a receiving substrate. In one particular example of the present invention, the plurality of elements are in a slurry. These elements fall into receiving regions on a template. These elements are then directly transferred to a receiving substrate by placing the template onto the substrate. The elements in the template face a surface of a substrate and the template or the elements contact the substrate. The elements may create recessed regions in the receiving substrate. The template is then removed and elements remain in the receiving substrate.
While an array of components (e.g. display components) for an assembly have been described as examples of the invention, an array of other assemblies such as x-ray detectors, radar detectors, micro-electro-mechanical structural elements (MEMS) or, generally, an assembly of sensors or actuators or an assembly of circuit elements also may be produced using the claimed invention. Thus, for example, flexible antennas, other sensors, detectors, or an array of circuit elements may be fabricated using one of the embodiments of the inventions. Other aspects and methods of the present invention as well as apparatuses formed using these methods are described further below in conjunction with the following figures.